The invention relates to an electrical machine and to a vehicle equipped with the electrical machine.
During operation of an electrical machine, such as a generator or an electric motor for example, heat is released in the electrical machine, wherein the release of heat leads to an increase in the temperature of the electrical machine. As a result, the maximum permissible temperature for the electrical machine leads to limiting of the power which can be delivered by the electrical machine over the long term. Therefore, it is necessary to cool the electrical machine during operation thereof. In so doing, cooling of the rotor of the electrical machine is particularly difficult.
The rotor is conventionally cooled by the rotor being equipped with a shaft of hollow design within which a liquid flows during operation of the electrical machine. However, a disadvantage of this is that there is a long heat-conducting path from the radial outer side of the rotor to the liquid. In addition, the surface which is arranged in the interior of the shaft, which comes into contact with the liquid and via which the heat is transmitted from the rotor to the liquid is small. In addition, in the event of a laminated core being arranged on the shaft, the boundary area between the shaft and the laminated core constitutes thermal resistance to the conduction of heat. As a result, cooling of the rotor with a shaft of a hollow design is disadvantageously ineffective overall.
The object of the invention is therefore to provide an electrical machine and a vehicle equipped with the electrical machine, wherein the electrical machine, in particular the rotor thereof, can be cooled effectively.
The electrical machine according to the invention has a rotor with a hollow shaft which, in its interior, delimits a hollow shaft axial channel which extends in the axial direction and into which a cooling fluid can flow during operation of the electrical machine, a laminated rotor core which is fitted radially on the outside of the hollow shaft and has two axial end sides, and an axial channel which is delimited by the laminated rotor core, extends in the axial direction from one of the two end sides of the laminated rotor core to the other of the two end sides of the laminated rotor core and is connected in a fluid-conducting manner to the hollow shaft axial channel, so that, during operation of the electrical machine, the cooling fluid can flow from the hollow shaft axial channel, via the axial channel, to the end sides and can flow radially to the outside downstream of the axial channel owing to centrifugal force. As a result, the cooling fluid comes into direct contact with the laminated core and can therefore effectively cool said laminated core. In addition, the boundary area between the hollow shaft and the laminated rotor core as a barrier to the conduction of heat to the cooling fluid no longer exists. In addition, it is possible to arrange the axial channel in such a way that the heat-conducting path to the cooling fluid within the rotor is short, as a result of which the cooling is likewise effective. Since the cooling fluid is returned via the laminated core, a return within the shaft is not necessary, and therefore the shaft can be designed to be short in the radial direction.
The electrical machine preferably has a stator which is arranged radially outside the rotor, a laminated stator core which has two axial end sides, and has a winding of electrical conductors, wherein the axial end sides of the laminated stator core are arranged in alignment with the axial end sides of the laminated rotor core and the electrical conductors exit from the laminated stator core at the axial end sides of the laminated stator core and form end windings radially outside the laminated stator core, so that the cooling fluid which can flow radially to the outside downstream of the axial channel can hit the end windings of the stator and therefore can cool said end windings. Therefore, the cooling fluid is used in order to cool both the rotor and also the end windings of the stator.
It is preferred that the axial channel is arranged between the hollow shaft and the laminated rotor core and is delimited by the hollow shaft and the laminated rotor core. Therefore, the cooling fluid which flows in the axial channel during operation can cool both the hollow shaft and also the laminated core. In this case, it is preferred that the hollow shaft and/or the laminated rotor core have a cutout, which cutouts form the axial channel.
As an alternative, it is preferred that the axial channel is delimited by the laminated rotor core on the inside and on the outside in the radial direction. Therefore, the laminated rotor core can be particularly effectively cooled. It is particularly preferred that the axial channel is arranged in the center between the radial inner side and the radial outer side of the laminated rotor core. Therefore, the heat-conducting paths to the axial channel within the laminated rotor core can be minimized.
A plurality of axial channels is preferably provided, which axial channels are arranged in a uniformly distributed manner in the circumferential direction. As a result, the rotor can be cooled in a uniform manner in the circumferential direction, as a result of which particularly hot points in the rotor can be avoided.
It is preferred that the rotor has a radial channel via which the axial channel is connected in a fluid-conducting manner to the hollow shaft axial channel. If the electrical machine has a plurality of axial channels, a respective radial channel can be provided for each of the axial channels, which radial channel connects the respective axial channel in a fluid-conducting manner to the hollow shaft axial channel.
The laminated rotor core usually has a cylindrical inside diameter which is somewhat smaller than the corresponding outside diameter of the rotor shaft. When the laminated core is shrink-fitted onto the rotor shaft, a rotationally fixed mechanical press-fit is established by thermal widening due to heating of the rotor laminate and/or cooling of the shaft. However, very accurate manufacturing tolerances and a slow and expensive furnace process are required for this purpose.
As an alternative, the individual laminates of the laminated rotor core can have a large number of cutouts which are distributed around the inside diameter. This creates a serrated pattern which interrupts the otherwise customary circular hole. In this case, the serrations are advantageously arranged in such a way that a cutout and a serration always come to lie one above the other when the laminates are stacked to form the laminated core. This has the advantage that the serrations of the laminates can yield when said laminated core is mounted on the shaft and, as a result, the laminated core and the rotor shaft can be joined when there are relatively small temperature differences, this simplifying and accelerating the process. In addition, the fluid-carrying axial channels can also be integrated in a simple manner at the same time as when the serrations/cutouts are produced.
It is preferred that the electrical machine has a machine housing which houses the rotor and the stator. As a result, the rotor and the stator can be protected against environmental influences and, in addition, the cooling fluid which exits from the end sides of the laminated rotor core can be captured. In this case, it is preferred that the machine housing has a passage hole which is arranged at the lower end of the machine housing and via which the cooling fluid can exit from the machine housing. Therefore, the cooling fluid which exits from the end sides of the laminated rotor core can be collected and then can flow back into the hollow shaft.
The machine housing preferably has a housing cooling channel through which a further cooling fluid can flow for the purpose of cooling the machine housing; in particular the electrical machine is designed for a mixture containing water and glycol to flow through the housing cooling channel.
Therefore, the cooling fluid which exits from the end sides of the laminated rotor core can be cooled and can therefore already once again be suitable to flow into the hollow shaft for the purpose of renewed cooling of the electrical machine.
It is preferred that the cooling fluid is electrically non-conductive. Therefore, the end windings themselves can then be cooled using the cooling fluid if the electrical conductors of the end windings are not electrically insulated. The cooling fluid is preferably an oil, in particular a transmission oil.
The electrical machine is preferably an electric motor, in particular for a vehicle.
The vehicle according to the invention has the electrical machine according to the invention, wherein the vehicle has a conveying device which is designed for the cooling fluid to flow into the hollow shaft, wherein the conveying device is designed, in particular, to convey a transmission oil of the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.